Fetuses with severe diaphragmatic hernia, who would be expected to die, have survived after successful surgical repair before birth. Although the early experience with 27 cases of open fetal surgery for a variety of lesions suggests that hysterotomy is safe for the mother and her reproductive potential, the efficacy of this invasive therapy for any given disease process cannot be established without a property controlled prospective trial. Despite the ethical, logistical, and financial difficulties of assigning or withholding an innovative surgical procedure for a life threatening fetal condition, we believe that it is imperative to establish the place of this promising new therapy early in its development, before it becomes established without being scientifically tested. We propose to perform a clinical trial to assess the efficacy and safety of open fetal surgery in treating severe cases of fetal diaphragmatic hernia. This will be a randomized control trial comparing two groups: those receiving open fetal surgery (innovative treatment group) and those receiving standard perinatal management (standard treatment group). The sample populations are subgroups of fetuses with diaphragmatic hernia selected using criteria developed in previous experimental and clinical studies. Fetuses with isolated left diaphragmatic hernia with a large volume of viscera including stomach incarcerated in the chest before 30 weeks gestation are candidates. The primary outcome variable is neonatal mortality. Secondary outcome variables are parameters reflecting long-term morbidity, mortality and cost analysis. Statistical analysis will use Chi- square for comparison of neonatal mortality and dichotomous secondary outcome variables. Student's t-test and the Mann-Whitney test will be used for continuous secondary outcome variables. Analysis will employ an intention to treat modification and provisions will be made for limb closure if statistically significant differences in primary outcome occur between the groups or if maternal mortality occurs in the group randomized to fetal surgery.